Notes Changing Atomic Models

Name Class Date Notes – Changing Atomic Models

A ______is a visual, verbal or mathematical explanation of how phenomena occur or how data and events are related. Because atoms are so small, models are helpful to explain their structure. An ______is the smallest part of an ______that still retains the properties of that element. As we have learned more about the atom, we have had to update our models of it. This outline traces the atomic model from the ancient Greeks to our modern model.

Ancient Greek philosophy I. The Greek model In 4 B.C. ______said matter was composed of small particles he called ______.

______disagreed with Democritus. He said all matter was composed of four elements: ______, ______, ______, and ______. His idea survived for 2000 years.

Antoine Lavoisier (1743-1794) Lavoisier refined experimentation by making precise measurements of the mass changes in chemical reactions. He is known as the ______.

John Dalton, the father of the modern atomic model By the late 1700’s scientists were doing quantitative studies of chemical reactions. These experiments led to the discovery of basic laws, which included the ______, the ______, and the______. To explain these laws, Dalton proposed his atomic model that included: 1. 2. 3. 4. 5.

William Crookes, inventor of the ______In 1870, Crookes developed the ______. This invention eventually helped lead to the discovery of the ______and the ______.

J. J. Thomson, discoverer of the ______A. Advances in technology made possible experiments to look closer at the atom. These included the invention of the vacuum pump and Crooke’s tube (cathode ray tube, CRT). B. Thomson studied the results of running electrical currents through small amounts of gas in a sealed glass tube. He noticed a stream of particles he called ______that would change direction because they were bent by magnets. Since the beam bent towards the ______plate, he concluded that the beam was composed of ______particles. He then determined the particles to be 2000 times smaller than the Hydrogen atom. The particles were called ______. C. A “picture” of Thomson’s model, also called the ______:

D. Because the atom is electrically ______, leftover particles must be ______. Thomson concluded that the positive particle was the same size as a hydrogen atom. Particles were named ______.

Sir James Chadwick, discoverer of the ______The mass of the atom was ______the size of the proton. Chadwick confirmed the presence of a third particle with ______and ______as a proton. It was called a ______. .

Ernest Rutherford, discoverer of the ______A. Ernest Rutherford aimed alpha particles from a radioactive source at thin metal foil. He expected the alpha particles to

B. Sketch the setup of Rutherford’s experiment, showing the paths of some alpha particles. C. Rutherford concluded that atoms contain

The negative electrons in an atom move around this like

D. Thomson’s atomic model had to be revised because it could not explain

E. A “picture” of Rutherford’s model:

Neils Bohr, discoverer of the quantum II. Bohr’s model A. Rutherford’s model could not explain some observations. B. Bohr proposed that electrons

C. A “picture” of Bohr’s model:

The modern model : Schrödinger III. The quantum model (also called the quantum mechanical or wave mechanical model) A. The quantum model is a model that uses equations to calculate where in an atom an electron is likely to be found. B. A “picture” of the quantum model: